In the construction of portable cold storage cabinets which use a source of liquified gas such as liquified nitrogen to obtain refrigeration, it is common for the liquified gas or nitrogen to be contained within a pressurized vessel and for the vapor to be supplied to a cold storage cabinet or chamber through a line having a valve controlled by a temperature sensing system. For example, U.S. Pat. Nos. 3,410,109, No. 3,693,371, No. 4,580,411 and No. 4,833,892 disclose different forms of cooling or freezing cabinets defining compartments which are refrigerated by means of a tank of liquified gas, usually liquified nitrogen which is commonly available. The vapor from the liquified nitrogen is directed from the upper portion of the supply tank to a perforated tube within the upper portion of the cooling or freezing chamber, and a thermostatic valve system controls the flow of vapor into the chamber according to the temperature desired within the chamber.
It has been determined that this form of refrigeration system is not very efficient since the nitrogen vapor quickly returns to the atmosphere without absorbing the maximum amount of heat per gallon of liquid nitrogen. In addition, the use of the temperature responsive control valve system and the pressure vessel for the liquified nitrogen add significantly to the cost of constructing, operating and servicing of the refrigeration system, thus making the liquified gas refrigeration system undesirable for many applications where refrigeration is obtained with solidified carbon dioxide or dry ice.